Mouthwashes have long been used as an adjunct to toothbrushing to achieve good oral oral hygiene. Essential oils containing mouthwashes have demonstrable antimicrobial activity and they have been studied and comercialised.

The main aim of this review was to assess the efficacy of mouthwashes containing essential oils (EO) as adjuncts to daily mechanical plaque control.

Methods

Searches were conducted in the Medline, Embase, LILACS and Scopus databases. Randomised controlled trials (RCTs) with a minimum of 6 months follow up of daily use of EO compared with placebo, flossing or cetylpyridinium chloride (CPC) as adjuncts to mechanical plaque control were considered.

Studies were screened independently by 3 reviewers and quality assessed using the Cochrane risk of bias tool. Dental Plaque was summarised using the Quigley-Hein Index (QHI) modified by Turesky. Gingivitis was summarised using three indices: the Gingival Index (GI) by Loe and Silness, the Modified Gingival Index (MGI), and bleeding upon probing. Mean and standard deviations were reported and meta-analysis conducted. Sources of effect modification were investigated using meta-regression.

Results

16 studies involving a total of 4016 patients were included.

A majority of the studies involved Listerine Antiseptic ®

11 studies tested EO as adjuvant for daily oral hygiene habits;5 provided some oral hygiene instruction to be applied during the study period.

The quality of the studies was assessed as moderate to low.

Meta-analysis of 14 studies found mouthwashes containing EO were statistically superior regarding the reduction of plaque than placebo.

Weighted mean difference [WMD] (95%CI)

Quigley-Hein Index (QHI)

-0.86 (-1.05 to -0.66)

Modified Gingival Index (MGI),

-0.52 (-0.67 to -0.37)

Gingival Index (GI)

-0.24 (-0.46 to -0.01)

Bleeding on probing

-0.16 (-0.22 to -0.06)

Meta-analysis (4 studies) found that compared with CPC, EO resulted in statistically lower levels of plaque and gingivitis

Weighted mean difference [WMD] (95%CI)

Quigley-Hein Index (QHI)

-0.75 (-0.89 to -0.61)

Modified Gingival Index (MGI),

-0.52 (-0.62 to -0.42)

A meta-analysis (4-studies) looking at the impact in interproximal areas only found significantly larger decrease in favour of the EO group.

Weighted mean difference [WMD] (95%CI)

Quigley-Hein Index (QHI)

-0.95 (-1.26 to -0.63)

Modified Gingival Index (MGI),

-0.34 (-0.53 to -0.15)

Meta-regression indicated that heterogeneity in the plaques scores was explained by the percentage of males and supervision of mouthwash use. While provision of oral hygiene instruction explained the heterogeneity in gingivitis scores.

Conclusions

The authors concluded:-

in patients with gingivitis, EO- containing mouthwashes are more efficacious for the reduction of plaque and gingival inflammation than mechanical plaque control either alone (placebo) or in combination with mouthwashes with CPC. The expected benefits may be clinically relevant and may be also observed in the interproximal area.

Comments

This systematic review has employed a good search strategy and employed standard review protocols. It found an estimated benefit for plaque reduction of around 32% and 24% for gingivitis in favour of EO mouthwash compared with placebo. The review also suggests a benefit in favour compared with CPC mouthwash, although only 4 studies were available for this comparison. The meta-analyses displayed high levels of heterogeneity but meta-regression suggested that this could be largely explained by supervision of use, % of males and provision of oral hygiene instruction. In interpreting the the findings it is worth noting that the quality of the studies was only moderate to low and all of the studies were industry funded.

Derek Richards is the Director of the Centre for Evidence-based Dentistry, Editor of the Evidence-based Dentistry Journal, Consultant in Dental Public Health with Forth Valley Health Board and Honorary Senior Lecturer at Dundee & Glasgow Dental Schools. He helped to establish both the Centre for Evidence-based Dentistry and the Evidence-based Dentistry Journal. He has been involved with teaching EBD and a wide range of evidence-based initiatives both nationally and internationally since 1994.